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Abstract:Ternary intermetallic A-B-C systems sometimes have unexpected behaviors. The present paper examines situations in which there is a tendency to simultaneously form the compounds ABx, ACx and BCx with the same crystal structure. This causes irregular shapes of the phase homogeneity domains and, from a structural point of view, a complete reversal of site occupancies for the B atom when crossing the homogeneity domain. This work reviews previous studies done in the systems Fe-Nb-Zr, Hf-Mo-Re, Hf-Re-W, Mo-Re-Zr, Re-W-Zr, Cr-Mn-Si, Cr-Mo-Re, and Mo-Ni-Re, and involving the topologically close-packed Laves, χ and σ phases. These systems have been studied using ternary isothermal section determination, DFT calculations, site occupancy measurement using joint X-ray, and neutron diffraction Rietveld refinement. Conclusions are drawn concerning this phenomenon. The paper also reports new experimental or calculated data on Co-Cr-Re and Fe-Nb-Zr systems.